Transmission Loss Analysis through Porous Laminated Glass using Transfer Matrices

Reduction of noise transmitted through laminated glass with interlayer is of interest to vehicle applications. Altering the structure of the interlayer can impact sound transmission loss particularly at the coincidence frequency. This study investigates the feasibility of including a porous layer within the laminated glass to act as an acoustic damper. To understand the underlying physics controlling transmission loss in laminated glass design, an approach utilizing transfer matrices is used for modeling each layer in the laminated glass. These transfer matrices are used to relate the acoustic characteristics of two points within a layer. For any two layers in contact, an interface matrix is defined that relates the acoustic fields of the layers depending on their individual characteristics. The solid layer is modeled as an elastic element and the sound propagation through the porous materials is described using the Biot theory. The effect of the variation in porosity on Poisson's ratio is incorporated in the porous model to calculate transmission loss. This study focuses on the effect that the porous layer has on the transmission loss at the coincidence frequency and at 9000 Hz. Porosities below 60% do not have a major effect on the transmission loss at the coincidence frequency. At porosities greater than 80%, the increased air content within the pores plays a major role in reducing the transmission loss and decoupling the layers of glass. A porous layer with close to 70% porosity is found to be optimal for improving transmission loss over the entire frequency range of interest spanning from 1000 Hz to 9000 Hz.